1. Field of the Invention
This invention relates to the field of data processing systems. More particularly, this invention relates to detection of spurious activity within a circuit.
2. Description of the Prior Art
Techniques exist for protecting secure systems such as smart cards and detecting signals that may indicate that the card is under attack. These can take the form of mechanical protection mechanisms, whereby if the casing around the smart card is damaged ingress of UV light causes the circuit to be damaged such that no data can be derived from it. Additionally they can be protected by having circuits for detecting a drop in a voltage line indicating a probe wire trying to force a value, or by having additional logic to detect if invalid conditions occur such as non-secure accesses trying to access a secure address space.
These protection systems primarily detect logical errors during processing or integrity violations by mechanical observations.
The Razor project at ARM provides a circuit level technique for detecting when a circuit has not reacted fast enough for the clocking speed used.
It would be advantageous to use circuit level techniques to detect unexpected behaviour or spurious signals in a circuit.